1. Field of the Invention
The present invention relates to scanners and, more particularly to scanners having multiple arrays wherein an electronic image of an original document is generated from the arrays.
2. Description of The Prior Art
The use of scanners for generating electronic images of an original document is well known in the prior art. Prior art scanners may be classified into two groups. The so called low resolution scanners and the so called high resolution scanners.
In the low resolution scanners a straight line of information on an original document is projected onto a linear diode array. The linear array outputs a video signal representative of the line of information on the original. With the low resolution scanners there is a one to one relationship between the length of the line of information on the original document and the length of the array which generates the video signal. In other words, the length of the array spans the width of a line of information on the original document. Thus a single linear array is used to project a line of data from an original document.
With the high resolution scanners two or more linear arrays, each including a plurality of serially configured picture elements, are used for generating the video signal for a straight line of data on an original document. In order to achieve the high resolution each character on a straight line of an original document is divided or partitioned into a plurality of Picture Elements (hereinafter called pixels or pel). A typical pel size is within the range of several microns. Each pel in the character is projected onto a pel or element in the linear arrays. As such, a relatively large number of diodes are needed to reproduce a video signal representative of a straight line of data on an original document.
It would be desirable to have the large number of elements required for a high resolution scanner packaged in a single linear array so that the array spans the width of a line on an original document. However, due to limitations imposed by the physical size of the scanner, the mechanical configuration of the arrays and, more important, due to limitations imposed by the solid state or semi-conductor technology the number of pixels positioned linearly on a substrate (that is the length of an array) is fewer than the number of diodes necessary to reproduce a high resolution copy of an original document. In other words, the length of a linear array is shorter than the width of a data line on an original document.
The aforementioned imposed limitations are overcome by projecting a straight line of a document onto a plurality of linear arrays. With respect to the straight line of data, running from left to right on a page, the arrays are positioned in an over-lapping offsetting fashion. Stated another way, in order to generate a video signal representative of a straight line of data extending from a left margin to a right margin of an original document, a first linear array is positioned so as to cover a portion of the line. A second linear array is positioned so that the beginning pixels in the second linear arrays overlap with the ending pixel of the first linear array.
Likewise, a third through N linear array is arranged in a fashion similar to that described for the first and second arrays (that is overlapping arrangement between consecutive arrays) until the line on the original document is covered. Although the arrays do not lie in the same plane, usually the arrays are offset, with respect to one another, in the direction of scan. Also the arrays are overlapped in a direction parallel to a line on the original document. By way of prior art example, U.S. Pat. Nos. 4,005,285 and 4,092,632 give a more detailed description of a multiple array scanner.
One type of problem which is associated with the prior art multiple array scanners is the so called abutment problem. The abutment problem usually occurs at the junction point or crossover point of successive arrays. The abutment problem generally manifests itself in two forms. In one form the video information at the crossover point is redundant. The redundant information arises because for some finite period of time common information from a line on a document is projected onto the overlapped elements of the arrays. The other form by which the alignment error manifests itself is that of separation. This means that the video output from succeeding arrays are separated by a gap.
In order to effectuate abutment between data outputted from the different arrays used for scanning, a straight line of an original document, a vernier scale, is fabricated on one of the arrays. The vernier scale is located at the overlapping portion of the arrays. The vernier scale is achieved by placing the photosensitive elements of the verniered section on a center-to-center distance which is shorter than the center-to-center distance between the non verniered section of the arrays. The reduction in center-to-center distance between elements in the verniered section of the array provides at least one point where the arrays are in alignment. The point is called the crossover point. The crossover point is determined by microscopic examination of the arrays and moving one of the arrays to achieve abutment. By way of example, a more detailed description of the prior art method of correcting abutment is given in the aforementioned U.S. Pat. No. 4,092,632.
Although the prior art approach to correcting abutment error associated with multiple array scanners appears to perform satisfactorily, it is lacking in some respect. For example, the prior art requires a physical orientation of the arrays to correct for abutment. The frequency with which abutment is needed may influence the throughput from the scanner since a trained technician is needed to make the necessary adjustment.
Moreover, in order to correct for abutment at least one of the arrays has to be custom made in order to have the reduced center-to-center distance needed in the verniered portion of the array. As is well known to those skilled in the art, custom built electronic components tend to be much more expensive than off the shelf components. Expensive components tend to increase the overall cost of the system.